trace-cmd: Handle junk on last page for tracecmd_read_cpu_last()

If the last page (or last pages) have just junk on it (timestamps
and discarded events), tracecmd_read_cpu_last should not return NULL.
It needs to test previous pages.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 21 insertions, 3 deletions

diff --git a/trace-input.c b/trace-input.c
index 31bcc55..40233c9 100644
--- a/trace-input.c
+++ b/trace-input.c
@@ -1006,7 +1006,7 @@ struct record *
 tracecmd_read_cpu_last(struct tracecmd_input *handle, int cpu)
 {
         struct record *record = NULL;
-        off64_t offset;
+        off64_t offset, page_offset;
 
         offset = handle->cpu_data[cpu].file_offset +
                 handle->cpu_data[cpu].file_size;
@@ -1016,9 +1016,14 @@ tracecmd_read_cpu_last(struct tracecmd_input *handle, int cpu)
         else
                 offset -= handle->page_size;
 
-        if (get_page(handle, cpu, offset) < 0)
+        page_offset = offset;
+
+ again:
+        if (get_page(handle, cpu, page_offset) < 0)
                 return NULL;
 
+        offset = page_offset;
+
         do {
                 free_record(record);
                 record = tracecmd_read_data(handle, cpu);
@@ -1026,7 +1031,20 @@ tracecmd_read_cpu_last(struct tracecmd_input *handle, int cpu)
                         offset = record->offset;
         } while (record);
 
-        return tracecmd_read_at(handle, offset, NULL);
+        record = tracecmd_read_at(handle, offset, NULL);
+
+        /*
+         * It is possible that a page has just a timestamp
+         * or just padding on it.
+         */
+        if (!record) {
+                if (page_offset == handle->cpu_data[cpu].file_offset)
+                        return NULL;
+                page_offset -= handle->page_size;
+                goto again;
+        }
+
+        return record;
 }
 
 /**